African dust impact on the size distribution of aerosols in the Caribbean: Observations from Atmospheric Observatory in Cabezas de San Juan, Puerto Rico

Each year Puerto Rico receives large amounts of African dust particles that are carried away by the trade winds from the North African desert to the Caribbean, particularly during the summer months. This dust consists of irregular particles with varying sizes. Particle size is a fundamental parameter when it comes to analyzing and predicting atmospheric lifetime, transport processes, and how these can have an impact on climate and ecosystems. The size distribution depends on the processes in which the aerosols are suspended and transported; therefore, a measure of this distribution can be key in determining the source of the aerosol. Here we present the results on the size distribution of aerosol measurements obtained in the summer months of June and July, 2012 at the atmospheric observatory of Cabezas de San Juan in Fajardo, PR. We performed in-situ measurements of size distribution using a Scanning Mobility Particle Sizer and an Optical Particle Counter, with measuring size ranges of Dp 0.01 to 1 µm and Dp 0.25 to 32 µm, respectively. During very hazy days we observed a noteworthy increase of the concentration of coarse particles (Dp > 1 µm), more notably for particles with Dp between 5 and 7 µm. The presence of African dust was supported using Saharan Air Layer images, measurements of aerosol optical thickness (AOT), air mass back-trajectories calculated with the NOAA HYSPLIT model, SKIRON and NAAPS dust forecasts, and filter color of samples obtained through in-situ measurements with Stacked Filter Units (SFU). Detailed results will be presented at the meeting.